title: Pharmacological and local toxicity studies of a liposomal formulation for the novel local anaesthetic ropivacaine.
abstract: This study reports an investigation of the pharmacological activity, cytotoxicity and local effects of a liposomal formulation of the novel local anaesthetic ropivacaine (RVC) compared with its plain solution. RVC was encapsulated into large unilamellar vesicles (LUVs) composed of egg phosphatidylcholine, cholesterol and alpha-tocopherol (4:3:0.07, mole %). Particle size, partition coefficient determination and in-vitro release studies were used to characterize the encapsulation process. Cytotoxicity was evaluated by the tetrazolium reduction test using sciatic nerve Schwann cells in culture. Local anaesthetic activity was assessed by mouse sciatic and rat infraorbital nerve blockades. Histological analysis was performed to verify the myotoxic effects evoked by RVC formulations. Plain (RVC(PLAIN)) and liposomal RVC (RVC(LUV)) samples were tested at 0.125%, 0.25% and 0.5% concentrations. Vesicle size distribution showed liposomal populations of 370 and 130 nm (85 and 15%, respectively), without changes after RVC encapsulation. The partition coefficient value was 132 +/- 26 and in-vitro release assays revealed a decrease in RVC release rate (1.5 fold, P < 0.001) from liposomes. RVC(LUV) presented reduced cytotoxicity (P < 0.001) when compared with RVC(PLAIN). Treatment with RVC(LUV) increased the duration (P < 0.001) and intensity of the analgesic effects either on sciatic nerve blockade (1.4-1.6 fold) and infraorbital nerve blockade tests (1.5 fold), in relation to RVC(PLAIN). Regarding histological analysis, no morphological tissue changes were detected in the area of injection and sparse inflammatory cells were observed in only one of the animals treated with RVC(PLAIN) or RVC(luv) at 0.5%. Despite the differences between these preclinical studies and clinical conditions, we suggest RVC(LUV) as a potential new formulation, since RVC is a new and safe local anaesthetic agent.
authors.affiliation: Department of Biochemistry, Institute of Biology, State University of Campinas - UNICAMP, Campinas, SP, Brazil. draraujo2003@yahoo.com.br
authors.forename: Daniele Ribeiro
authors.initials: DR
authors.lastname: de Araujo
authors.forename: Cíntia Maria Saia
authors.initials: CM
authors.lastname: Cereda
authors.forename: Giovanna Bruschini
authors.initials: GB
authors.lastname: Brunetto
authors.forename: Viviane Urbini
authors.initials: VU
authors.lastname: Vomero
authors.forename: Amauri
authors.initials: A
authors.lastname: Pierucci
authors.forename: Humberto Santo
authors.initials: HS
authors.lastname: Neto
authors.forename: Alexandre Leite Rodrigues
authors.initials: AL
authors.lastname: de Oliveira
authors.forename: Leonardo Fernandes
authors.initials: LF
authors.lastname: Fraceto
authors.forename: Angélica de Fátima de Assunção
authors.initials: Ade F
authors.lastname: Braga
authors.forename: Eneida
authors.initials: E
authors.lastname: de Paula
mesh_terms: D000577:Amides / Q000008:administration & dosage / Q000494:pharmacology* / Q000633:toxicity; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology* / Q000633:toxicity; D000818:Animals; D002784:Cholesterol / Q000737:chemistry; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004531:Eggs; D008081:Liposomes; D008297:Male; D051379:Mice; D009407:Nerve Block / Q000379:methods*; D010316:Particle Size; D019999:Pharmaceutical Solutions; D010713:Phosphatidylcholines / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D000077212:Ropivacaine; D012583:Schwann Cells / Q000187:drug effects / Q000378:metabolism; D018675:Toxicity Tests; D024502:alpha-Tocopherol / Q000737:chemistry
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D008081:Liposomes; D019999:Pharmaceutical Solutions; D010713:Phosphatidylcholines; D000077212:Ropivacaine; D002784:Cholesterol; D024502:alpha-Tocopherol